I've always wanted to play the "Enchantment Under the Sea Dance" sequences of both films at the same time to see how well Robert Zemeckis did with the continuity, but I didn't care enough to buy another VCR or DVD player. Fortunately, however, the internet keeps making dreams come true, and now we can see a split screen showing both films, and check to see how they match up. A guy named Matthew Muhl did the job for us and synced up the 15-minute-long section of the films, and it appears the makers of the sequel were mostly spot on, with the few exceptions being performance based (watch Lea Thompson as she tells Marty that George will drive her home). The two films aren't time-exact, but movies rarely represent real time, so that isn't an error on the part of the filmmakers.
The script supervisors on BTTF2 were Marion Tumen and Alan Greedy -- perhaps they should have been given a special Oscar for continuity.